A method of damping abnormal vibrations, also known as "bucking", which may occur in internal combustion einges of the spark-ignition kind, has been proposed in commonly assigned URBANEK German Paent DE 42 01 861 Cl, filed Jan. 24, 1992, to be published Feb. 4, 1993. In accordance with that disclosure, in the event of increasing engine speed, engine torque is reduced by retarding the ignition angle, and in the event of decreasing engine speed, engine torque is increased by advancing the ignition angle.
Engine speed fluctuations are detected by measuring any deviation in speed per unit of time, with a distinction being made simultaneously between bucking vibrations and acceleration intended by an operator. Where the change in speed is caused by bucking, the change in speed is quantified or weighted, and a corrective ignition angle of appropriate sign is added to the effective, normal ignition angle, i.e. ignition timing is either advanced or retarded.
In certain circumstances, damping of bucking or of abnormal vibrations upon detection of deviations in engine rotation may not be achieved sufficiently quickly since the anti-bucking control will not be effective until after the occurrence of initial deviations in speed. That may, however, adversely affect the performance of an internal combustion engine.